Manufacture of hydrated



Reissued October 5, 1948 UNITED STATES PATENT OFFICE MANUFACTURE OF HYDRATED POLYSILICATE Walter F. Wegst, Wyando Quartz Company, tion of Pennsylvania tte, Mich., and John H.

to Philadelphia N Drawing. Original No. 2,179,806, dated November 14, 1939,

8 Claims.

crystals having a diameter to 10 microns and containafter set forth and as claimed.

While several crystalline hydrates of sodium metasilicate and at least one crystalline hydrate of sodium sesquisilicate have been reported in the literature,

our knowledge of the field which includes high silica, ratios is very limited.

We have now drate having a ratio of NazO to S102 which lies We have further found this compound and have to which it may be put.

water of hydration. methods of preparing developed various uses Ser1al No. 111,556, November months, if a solution containing 11 per cent NazO and 32 per cent S102 is agitated and heated to temperatures of about to 85 C. over such a period of time. We have found that it usually requires several years for the spontaneous f0rmation of tetrasilicate crystals to occur in the same solution standing at room temperatures. When seed crystals are added to solutions capable of growing the crystals, however, propagation can be accomplished at a reasonable rate of speed provided operating conditions are properly chosen.

Our experiments indicate that the tetrasilicate crystals can be grown in any concentrated liquid silicate solution of high silica ratio containing the proper proportion of water and advantageously having a ratio of Na-zO to S102 ranging from about 1:2 to 1:11 or above. Best results have been obtained when the SiOz in this ratio has been above 2.4. The amount of water present should not exceed about 75 to per cent by weight. As examples of solutions which are capable of growing crystals of the new tetrasilicate, there may be mentioned the following six sodium silicate solutions which have been employed in practice in growing tetrasilicate crystals, these solutions containing NazO and SiOz in the precentages by weight as indicated: (1) 6.0% NazO, 23.6% SiOz; (2) 6.3% N320, 22.9% SiOz; (3) 8.3% NazO, 24.0% SiO2; (4) 9.4% NazO, 23.8% S102; (5) 11.0% NazO, 26.6% SiOz; (6) 13.7% NazO, 32.9% S102. The percentages of water in these solutions can be found b subtracting the percentages of NazO and SiOz from 100%. Our experiments indicate that temperatures ranging from about 0 to 100 C. can be employed in growing tetrasilicate crystals although we have obtained best results within the narrower range of from about 60 to 90 C.

In preparing the tetrasilicate crystals it is merely necessary to prepare a suitable sodium silicate solution, to add seed crystals thereto and then to allow he solution to stand for a sufficient length of time celerated by heating the solution to temperatures C. and by agitation. The optimum crystallizing temperature appears to be between about 75 and C. but even at this temperature it usually requires several days for the seed crystals to double in weight. The resulting magma of crystals from the mother liquor by filtration or by the use of a centrifuge, for example, and then washed with water. Since the crystals dissolve very little over 1 slowly at ordinary temperatures washed thoroughly if cold water crystals should then be dried at temperatures which are advantageously below 80 C., since under ordinary conditions they lose water rather rapidly above this temperature.

In order to dry the crystals rapidly they may be washed with any convenient water-soluble volatile solvent which will not react with the crystals. Alcohol followed by ether may be used although our experiments show that alcohol reacts to some extent with the crystals to form a gel coating.

The tetrasilicate crystals are usually obtained in extremely finely divided form. When examined under a low power microscope it is difficult to distinguish the shape of the crystals although their birefringence is plainly noticeable. The crystals usually vary in diameter from about 1 to 10 microns. When examined as to their optical properties it has been found that the crystals are either uniaxial or, if biaxial, {3 and 'y are practically identical. The elongation is 1, extinction parallel. or equals 1.4631003. 1 equals 1.4831003.

The crystals they may be is used. The

are stable in their mother liquor for periods of longer than one month when frozen in ice. They are also stable in solutions kept at 85 C. and have been kept at 95 C. for live hours with only partial solution. Th mother liquor used in these particular tests analyzed 9.38 per cent NazO, 25.41 per cent SiOz and 65.16 per cent H2O.

Our experiments show that the tetrasilicate crystals lose water on heating, even at fairly low temperatures. When dried at 62 C. for example, they retain from about 13 to 1'7 per cent of water. Heated at 80 C. there is an additional loss of a per cent of water. After drying at 100 C. there is somewhat less than 6 per cent of water remaining, while at 320 C. there still remains about 1.5 per cent of water. These eX- periments indicate the existence of several hydrates of the composition Na2OI4ASiO2IxI-I2O, having transition points lying between the temperatures of to 200 C. or above. The present invention provides methods of preparing such hydrates.

In obtaining proof of the chemical composition of the new crystals, several different methods of analysis were employed. Employing the socalled inert material method" (described in Treatise on Physical Chemistry by Hugh S. Taylor, D. Van Nostrand Co., Inc., New York, 2nd edition (1931), vol. I, page 560, last paragraph) for estimating the amount of mother liquor mixed with the crystals, we used sodium chloride as the inert material. In one analysis by this method we found the molecular ratios of Nazozsiozzl-lzo to be 1:3.9'71'700, while in a second test, in which a larger quantity of mother liquor was mixed with the crystals, we obtained ratios of l:4.09:7.57. Since the latter results included a greater experimental error due to the larger amount of mother liquor, the former values of the ratios are probably the more nearly correct. A direct analysis of the crystals, after washing with water to free them from mother liquor, gave a ratio of NazO to SiOz of 1:4.00. Three more recent analyses by the inert material method, using an improved technique in which the inert material was present during the growth of the crystals and which therefore took account of any mother liquor inclusions in the crystal masses, gave values of lNa2O:4.2SiO::3.9I-l2O;

and 1NazO:4.2SiOz:4.2H2O, respectively.

The above results were also checked by the so-called wet residue method of Schreinemaker, described in Z. Physikal. Chem., 11, '76 (1893) In these tests four sodium silicate solutions of different composition were prepared and tetrasllicate crystals were grown in each. The mother liquors and the wet residue of crystals were then analyzed. These data were then used, according to the method of Schreinemaker, to estimate the percentages of NazO present in the dry crystals. The results obtained for the four solutions gave percentages of 14.09%, 14.18%, 13.91% and 14.30%, respectively, for the NazO present in the dry crystals. This compares with a theoretical value of 14.47% NazO for the compound NazOz4SiOzz7HzO.

A number of more recent analyses by the wet residue method, using an improved technique in which the probable accuracy was about double that obtained in tests mentioned in the preceding paragraph, indicate that the composition of the new product lies between about and lNazO:4.3Si02:3.7H20. A series of analyses involving the steps of washing and pressing a magma of crystals between filter paper, followed by analysis of the pressed residue, indicates that the composition is between the values lNazO 1 4.33102. 3.7H2O

and 1N8.2OI4.5S1O223.5H2O. Experiments involving drying a Washed magma of crystals to constant weight followed by analysis, gave values indicating an average composition of The above data indicate that the crystals of the present invention correspond to a tetrasillcate having a composition lying between about lNazO 14.38102: 21-120 and lNazO 4.5Si0z 41-120, or, as an average value, INa2OI4.4SlO2Z3H2O. Of course the most accurate way of identifying crystalline compositions is by measurement of the refractive index of the crystals. These measurements have been made many times on different samples of our composition without finding any deviation from the crystal constants set out above. X-ray diffraction patterns have also been made on several different samples but no indication has been found that different crystal phases were present. From this it is concluded that we are dealing with a single crystal phase the chemical analysis of which is doubtless fixed but difilcult to determine with accuracy.

In one specific embodiment of the process of the present invention we took 29 kilograms of a silicate of soda solution containing 11 per cent NazO and 33 per cent of S102. We seeded this solution with a magma of crystals of tetrasilicate recovered from a previous operation weighing 3.25 kilograms and containing 22 per cent grams dry weight. This solution was stirred at high speed and maintained at a temperature of C. for 24 hours. tetrasilicate crystals were recovered from this solution, washed and dried, with a yield of 1,199 grams, representing 484 grams, dry weight, of crystals grown. There was a loss of weight by evaporation of the solution amounting to about modifications can be made in per cent. The liquid silicate going into the formation of the crystals amounted to 1.55 per cent.

In another operation we took 21 kilograms of the same silicate of soda solution and added a crystal sludge weighing 3.83 kilograms or 843 grams of crystals, dry weight. This mixture was agitated, but at a slower rate than in the preceding example, for a period of 7 days while the temperature was maintained at 70 C. In this case the dry weight of the crystals grown was 149 grams. The loss by evaporation amounted to about 10 per cent and the liquid silicate forming the crystals amounted to 0.6 per cent.

Our new tetrasilicate has characteristics which adapt it to many uses. Some of the uses for which it appears particularly adapted are as follows:

(1) As an ingredient for enamels adapted to provide silica in a readily fluxible form to make possible a high silica content in the enamel without release of gas.

As an ingredient of cements and concretes where a slowly soluble silica is desirable as a hardening agent, or where silica in more reactive form than pure quartz is required. As a means of purifying silicates and of obtaining highly siliceous silicates in pure form without the cost and danger of contamination inherent in the fusion process, and having the advantage of a fine state of subdivision Without the need of grinding and consequent contamination from that source. As a finely divided product which combines abrasives and cleansing properties either alone or as an ingredient of cleansing compositions.

It is likewise evident that the tetrasilicate can be employed in making up silicate solutions, that various uses which have been suggested previously for silicate solutions of similar compositions.

While we have described what we consider to be the best embodiments of our invention it will be obvious to those skilled in the art that various the procedure outspecifically, ranges of temperature, concentration, pressure, etc. from which the crystalline compound having the described properties will separate as a solid phase in contact with mother liquor, as understood under the principles of the phase rule. Modifications of our method which fall within the scope of the following claims we consider to be part of our invention.

What we claim is:

1. A crystalline product composed of fine crystals whose elongation is y, extinction parallel and wherein a equals 1463:.003, and 7 equals 1.4831003; said crystals having a molecular ratio of NazO to S102 of from 1:4.3 to 1:4.5 and containing approximately 2 to 4 molecules of water.

2. In the process of manufacturing crystalline silicates, the step which comprises seeding a sodium silicate solution, containing more SiOz than is represented by the molecular ratio of lNazO to 28102 and containing not substantially more than about 75 per cent of water, with crystals having a molecular ratio of NazO to S102 of from about 1:4.3 to 1:45 and containing approximately 2 to 4 molecules of water.

3. The process which comprises seeding a concentrated sodium silicate solution, having a molecular ratio of SiOz to NazO above about 2 to l, with crystals having a molecular ratio of Na2O to SiOz of from about 1:43 to 1:45 and containing approximately 2 to 4 molecules of water, and heating said solution within a temperature range of from about 60 to C. for a time sufficient to grow said crystals.

4. The process which comprises adding crystals, having a molecular ratio of NazO to S102 of from sodium silicate solution contaming S102 able for the growth of said crystals.

5. The process which comprises adding crystals, having a molecular ratio of Na20 to $102 of from ing said solution within the temperature range of about 75 C. and under conditions of agitation for a time sufiicient to grow said crystals.

7. The process which comprises heating a sodium silicate solution containing 8102 amount greater than that represented by the molecular ratio of tures ranging from about 60 conditions of agitation for a water.

8. The process which comprises heating crystals, having a molecular ratio of NazO to S102 of from about 1:4.3 to 1:4.5 and containing approximately 2 to 4 molecules WALTER. F. WEGST. JOHN H. WILLS.

REFERENCES CITED The following references are file of this patent:

of record in the Babor et al.: General College Chemistry, DD. 34-37. Pub. by Thomas Y. Crowell Co., New York, 1940.

Certificate of Correction Reissue No 23,043. October 5, 1948.

WALTER F. VJEGST ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 56, claim 8, after the word compounds insert containing water of hydration and; line 58, same claim, for the numeral 7 read .4;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 22nd day of February, A. D. 1949.

THOMAS F. MURPHY,

Assistant C'ommissioner of Patents. 

